1. Field of the Invention
This invention relates to a method and apparatus for determining the steering position of a vehicular steering mechanism. This method and apparatus are useful for controlling a vehicular suspension system or other automotive devices.
2. Disclosure Information
Adaptive automotive suspension systems are known in the art. An example of such a system is shown in U.S. Pat. No. 4,621,833, which is assigned to the assignee of the present invention. The system of the '833 patent, as well as other known adjustable suspension systems, adjusts the damping force produced by one or more suspension units according to a plurality of inputs from different sources within the vehicle. For example, it is known from the '833 patent to control suspension units by utilizing vehicle linear acceleration, braking, steering activity, vehicle speed, predicted lateral acceleration, and other inputs.
The use of steering angle sensors to provide steering input for the control of suspension units is commonly known. Systems employing fixed steering angle sensors are prone to failure due to misadjustment of the sensor inasmuch as precise angular measurements must be obtainable from such sensors if they are to be employed in systems capable of correcting or anticipating and preventing excessive roll of an automobile body during a cornering maneuver. Also, such sensors are unable to compensate for changes in wheel alignment due to impacts with road obstructions or wear within the steering mechanism. A related problem affects systems employing centrifugal force sensors inasmuch as such force cannot be sensed until it exists, and once such force has come into existence the vehicle's body will typically have assumed an attitude that can be corrected only by an active suspension device capable of exerting force independently of its velocity of operation. Thus, to be effective, a device for providing steering input to a control system for operating suspension units should anticipate lateral acceleration rather than merely sense acceleration. U.S. Pat. No. 4,621,833 discloses a steering center position algorithm and method for finding steering center position which is suitable for use in a system capable of anticipating lateral acceleration rather than merely sensing such acceleration.
The steering sensor system disclosed in U.S. Pat. No. 4,621,833 employs a software program in which steering center position is determined through the use of a fixed sample time detection scheme operating with variably-sized, circumferential window zones of operation of a steering shaft. Because the sampling time associated with the algorithm of U.S. Pat. No. 4,621,833 is fixed, the system disclosed therein has a limited capacity to deal with changes in steering center position.
The steering sensor system disclosed in U.S. Pat. No. 4,848,791, which is assigned to the assignee of the present invention, utilizes a software program in which steering center position is statistically determined over a fixed period of time sufficient to insure an accurate center position. This system takes an undue length of time to determine the center position and is further unable to continuously compensate for transient conditions, such as cross winds, road crown, and electronic component drift. Any combination of these can occur, thereby reducing the accuracy of the calculated instantaneous steering position, which is dependent on the underlying center position.
It is an object of the present invention to provide a method and apparatus for determining the center position of a vehicular steering mechanism which will rapidly determine a correct steering position when the vehicle system is first keyed on and which continuously updates that center position as time progresses until the vehicle is turned off.